Altered microstructural integrity of the white matter tracts in strabismus: A systematic tract-specific analysis over the whole brain
Hsien-Te Su1, Tzu-Hsun Tsai2, Yao-Chia Shih3, Yu-Shiang Tzeng4, Chien-Chung Chen4, and Wen-Yih Isaac Tseng1,5

1Institute of Medical Device and Imaging, National Taiwan University College of Medicine, Taipei City, Taiwan, 2Department of ophthalmology, National Taiwan University Hospital, Taipei City, Taiwan, 3Institute of Biomedical Engineering,National Taiwan University, Taipei City, Taiwan, 4Department of Psychology, National Taiwan University College of Science, Taipei City, Taiwan, 5Molecular Imaging Center, National Taiwan University, Taipei City, Taiwan


To investigate whether the white matter tracts are altered in patients with strabismus, we used diffusion spectrum imaging to measure microstructural property of 78 major white matter tracts, and compared the property between 12 patients with strabismus adults and 24 matched controls. As compared to the controls, patients showed differences with large effect sizes in the left vertical occipital fasciculus, callosal fibers to bilateral precuneus, callosal fibers to bilateral inferior parietal lobules, and the left superior longitudinal fasciculus I. The altered white matter tracts support the hypothesis of underlying microstructural changes of the visual pathways in strabismus.


Brain structure deficit has been implicated in the genesis of strabismus and in the mechanisms adopted to compensate for the visual disorder. We hypothesized that white matter fiber tracts may be also altered in strabismus. Therefore, we performed a tract-specific analysis of the whole brain to measure the microstructural properties of 78 major white matter tracts in a systematic way.


Subjects: Twelve patients with strabismus (age: 29.8± 6.56 years, 8 males and 8 females) and 24 age-matched neurotypical controls (age: 30.3± 4.53 years, 17 males and 7 females) were recruited in the study. All participants received clinical evaluations, refraction test, prism and cover testing and MRI scans. The grade of a diopter went higher as patients’ focal length got shorter; the higher the diopter correction, the more magnification patients needed to read or see things up close. Prism and cover testing was used to determine the amount of strabismus. A prism is held over the deviated eye and the eyes were alternately covered and the eye alignment was measured in different gaze directions, on head tilts, and at near.1 Imaging: MRI scans were performed on a 3T MRI system (TIM Trio, Siemens, Erlangen) with a 32-channel phased array coil. T1-weighted imaging utilized a 3D magnetization-prepared rapid gradient echo pulse sequence: TR/TE = 2000/3 ms, flip angle = 9o, FOV = 256 × 192 × 208 mm^3, matrix size = 256 × 192 × 208, and resolution = 1 x 1 x 1 mm^3. Diffusion spectrum imaging (DSI) used a twice-refocused balanced echo diffusion echo planar imaging sequence, TR/TE = 9600/130 ms, FOV = 200 x 200 mm^2, matrix size = 80 x 80, 39 slices, and 2.5 mm in slice thickness. A total of 102 diffusion encoding gradients with the maximum diffusion sensitivity bmax = 4000 s/mm^2 were sampled on the grid points in a half sphere of the 3D q-space with |q| ≤ 3.6 units. Analysis: We used whole brain tract-based automatic analysis to obtain a 2D connectogram for each DSI dataset.2 The connectogram provides generalized fractional anisotropy (GFA) profiles of 78 white matter tract bundles. We then averaged the tract means over all participants within each group and calculated the signed differences between patients and controls for each tract. We calculated the effect size3 to indicate the significance of the differences between the groups.


Patients with strabismus showed four tracts that were altered with effect sizes larger than 0.77. (Effect size > 0.8 is defined as large, (Table 1). These four tracts included the left vertical occipital fasciculus (VOF), callosal fibers to bilateral precuneus, callosal fibers to bilateral inferior parietal lobules, and the left superior longitudinal fasciculus I (SLF I), with the effect sizes being 1.26, 0.96, 0.77 and 0.77, respectively (Figure 1).


This is the first study to use tract specific analysis of the whole brain to systematically investigate the microstructural property of the fiber tracts in strabismus. Comparing to controls, four tracts are found to have differences with large effect sizes. These tracts are compatible with previous neuroimaging studies on brain structure and function in strabismus using various modalities. We found that patients with strabismus showed higher GFA values in the left VOF. The VOF connects the angular gyrus of the dorsal stream and the occipito-temporal sulcus of the ventral stream,4 and is also altered in patients with visual misalignment.5 We also found that the callosal fibers to bilatreral precuneus, callosal fibers to bilatereal inferior parietal lobules and the left SLF I had lower GFA values in patients with strabismus. Alvarez used fMRI to study the effects of an 18-hour vision therapy in patients of convergence insufficiency. They found a significant therapeutic effect on the activation in the precuneus area.6 The SLF I is one of the major fiber tracts that involves visual attention,7 and so altered SLF I might contribute to the failure of visual concentration in patients with strabismus. Bilateral inferior parietal lobules have been found in fMRI to maintain attention on current task goals around us,8 and are smaller in volume in patients with strabismus.9 In conclusion, the altered white matter tracts support the hypothesis of underlying microstructural changes of the visual pathways in strabismus.


No acknowledgement found.


1. Tsai T, Demer J. Nonaneurysmal Cranial Nerve Compression as Cause of Neuropathic Strabismus: Evidence From High-Resolution Magnetic Resonance Imaging. American Journal of Ophthalmology. 2011; 152(6):1067-1073.e2.

2. Chen Y, Lo Y, Hsu Y et al. Automatic whole brain tract-based analysis using predefined tracts in a diffusion spectrum imaging template and an accurate registration strategy. Human Brain Mapping. 2015; 36(9):3441-3458.

3. Cohen J. Statistical Power Analysis For The Behavioral Sciences. Hillsdale, N.J.: L. Erlbaum Associates; 1988.

4. Yeatman J, Weiner K, Pestilli F, Rokem A, Mezer A, Wandell B. The vertical occipital fasciculus: A century of controversy resolved by in vivo measurements. Proceedings of the National Academy of Sciences. 2014; 111(48):E5214-E5223.

5. Duan Y, Norcia A, Yeatman J, Mezer A. The Structural Properties of Major White Matter Tracts in Strabismic Amblyopia. Investigative Opthalmology & Visual Science. 2015; 56(9):5152.

6. Alvarez T, Vicci V, Alkan Y et al. Vision Therapy in Adults with Convergence Insufficiency: Clinical and Functional Magnetic Resonance Imaging Measures. Optometry and Vision Science. 2010; 87(12):E985-E1002.

7. Parks E, Madden D. Brain Connectivity and Visual Attention. Brain Connectivity. 2013; 3(4):317-338.

8. Singh-Curry V, Husain M. The functional role of the inferior parietal lobe in the dorsal and ventral stream dichotomy. Neuropsychologia. 2009; 47(6):1434-1448.

9. Yan X, Lin X, Wang Q et al. Dorsal Visual Pathway Changes in Patients with Comitant Extropia. PLoS ONE. 2010; 5(6):e10931.


Table1: Effect size in 78 tracts; Effect size>0.3 defined small difference; Effect size>0.5 defined medium difference; Effect size>0.8 defined large difference.

Figure 1: The left vertical occiptal fasciculus (red), the precuneus of corpus callosum (yellow), inferior parietal lobule of corpus callosum (green) and left superior longitudinal fasciculus I (blue) were shown significant difference.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)